1. Field of the Invention
The present invention relates to a Wireless Local Loop (WLL) system and, in particular, to a radio resources management method of a WLL system that is capable of managing radio resources efficiently.
2. Background of the Related Art
In general, a WLL system provides services such as voice communication, data communication, video communication, etc. to WLL subscribers by using Radio Frequency (RF) signals. A WLL system may typically be installed and operated in a region where it is difficult to install a wired telephone network.
A WLL system generally emulates a wired public telephone network by enabling local loop connections between a subscriber and the telephone network via radio communication channel rather than over wires.
FIG. 1 is a schematic block diagram illustrating a general WLL system. The WLL system includes a subscriber terminal 10, a Base Transceiver Station (BTS) 11 providing the wireless connection to a WLL subscriber, synchronous maintenance, allocation and release of communication channels, etc. with the user terminal 10 through wireless communication, a Base Station Controller (BSC) 20 controlling the position information and state information of a subscriber by connecting with the BTS 11 through a Pulse Code Modulation (PCM) link, and a Man-Machine Controller (MMC) 30 supporting the input of user data and display of the state of the WLL system.
The WLL system is, for example, installed and operated in a region where it is difficult to adapt a wire telephone network. To support various communication services in the region, generally a base transceiver station is installed and operated, as depicted in FIG. 1. The operator of the WLL system establishes a cell plan, including the base transceiver stations, and creates initial subscriber information designating a home base station to the WLL subscribers of cells 100˜300. The traffic volume of each cell can be set appropriately in consideration of the traffic characteristics of the region.
When subscriber information is created initially, the operator stores information of the home base station of each subscriber in a Data Base (DB) 20-1, of the BSC 20, through the MMC 30. A call processing processor 20-2 of the BSC 20 performs a call processing operation in accordance with various messages received from the subscribers and manages and updates position and state information of the subscribers stored in the DB 20-1. The position information is the position information of the subscriber terminal 10.
For example, when a power ON message or a subscriber position registration request message is received from the subscriber terminal 10, the call processing processor 20-2 of the BSC 20 manages the pertinent subscriber terminal 10 as being in an ATTACH/IDLE state. The subscriber position registration request message is periodically transmitted at a certain time interval. In addition, when a power OFF message is received from the subscriber terminal 10, the call processing processor 20-2 manages the subscriber terminal 10 as being in a DETACH/IDLE state. When a call processing request message is received, the call processing processor 20-2 manages the subscriber terminal 10 as being in an ATTACH/BUSY state, while performing operations such as a wireless contact, synchronous maintenance, allocation/release of communication channels, etc. As described above, when various messages are received from the subscriber terminal 10, the call processing processor 20-2 manages various subscribers efficiently by updating the position information and state information of the subscribers stored in the DB 20-1.
In the WLL system, there is a wireless region operated by the cell plan between a BTS and a terminal. An antenna of the BTS is placed so as to have constant directivity in consideration of the characteristics of the radio environment. However, because a BTS is always exposed to the natural environment, the directivity of the BTS antenna can be changed under the circumstances of rain, wind, etc. When the directivity of the antenna of the BTS 11 is changed, the BSC 20 may receive a request message transmitted from the terminal 10, not through the BTS 11 in the local cell in the region, but through a BTS 12 located in another cell. This may cause frequency loss and transmission delay and, accordingly, the communication quality in the wireless region and the reliability of the WLL system may be reduced.
In addition, the call processing processor 20-2 performs a call processing operation in accordance with a power ON/OFF message, a subscriber position registration request message, or a call processing request message received from the subscriber terminal 10. Additionally, it manages and updates the position and state information of a subscriber. However, the call processing operation can be performed only when a present subscriber terminal operates normally. When the subscriber terminal 10 operates abnormally, the WLL system not only can not appropriately manage the position and state information of a pertinent subscriber, in accordance with the plurality of request messages, but also can not take the necessary active measures corresponding to the abnormal state.
Accordingly, in the conventional WLL system, an abnormal state can not be sensed so that appropriate corrective action may be taken. When the radio resources allocated by the cell plan are in an abnormal state due to a change in the radio environment, the communication quality and reliability of the WLL system are reduced.